Production of complex beryllium hydrides

ABSTRACT

When subjecting a mixture of beryllium and an alkali metal aluminum complex of the formula 
     
         MAlR.sub.m H.sub.n 
    
     wherein M is an alkali metal, R is a hydrocarbyl group, m is an integer from 1 to 4, n is an integer from 0 to 3, the total of m and n being 4, to a pressurized atmosphere of hydrogen and an elevated temperature, a solid reaction product is produced. This product, composed of M 2  BeH 4  and other solid components, is mixed with an inert liquid diluent having a specific gravity above that of the M 2  BeH 4  but below that of essentially all of the other solid components. A separation is effected in this diluent between the M 2  BeH 4  and essentially all of such other solid components, and the M 2  BeH 4  is recovered.

INTRODUCTION

This invention relates to an improved process for the synthesis andrecovery of alkali metal beryllium tetrahydrides, such as Li₂ BeH₄, Na₂BeH₄, and the like

BACKGROUND

U.S. Pat. No. 3,647,399 to Ashby and Kobetz describes the firstsuccessful synthesis of the alkali metal beryllium tetrahydrides. Theprocess they employed involves the reaction of a beryllium dialkyl, BeR₂(R=alkyl of 1 to 10 carbon atoms), with a compound of the formula MAlR₃H, MAlR₂ H₂, or a mixture of both such compounds (M=alkali metal).

A more desirable process for the synthesis of alkali metal berylliumtetrahydrides involves subjecting a mixture of beryllium and an alkalimetal aluminum complex of the formula

    MAlR.sub.m H.sub.n

wherein M is an alkali metal, R is a hydrocarbyl group, m is an integerfrom 1 to 4, n is an integer from 0 to 3, the total of m and n being 4,to a pressurized atmosphere of hydrogen and an elevated temperature atwhich alkali metal beryllium tetrahydride of the formula M₂ BeH₄ isproduced. Such a process is described in detail in copending applicationSer. No. 566,193, filed Dec. 28, 1983 by Roy J. Laran and assigned tothe same assignee as the assignee of the present application.

THE DRAWING

The Figure of the Drawing depicts schematically one preferred processsequence of this invention.

THE INVENTION

The present process represents an improvement in the process set forthin the foregoing copending application, all disclosure of which isincorporated herein by reference as if fully set forth in the presentdisclosure.

More particularly, when the process of the copending application iscarried out either with or without an innocuous reaction diluent a solidreaction product is formed. This product is composed of dialkali metalberyllium tetrahydride, M₂ BeH₄, and other solid components such asalkali metal aluminum complexes (MAlR_(m) H_(n)), alkali metal hydride(MH), metallic beryllium, metallic aluminum, and the like.

In accordance with this invention the solid reaction product is mixedwith an inert liquid hydrocarbon or other inert diluent having aspecific gravity above that of the M₂ BeH₄ but below that of essentiallyall of the other solid components of the solid reaction product (i.e.,except for beryllium hydride, BeH₂, if present in the reaction product),and in this diluent a separation is effected between the M₂ BeH₄ andsuch other solid components. This makes possible the facile isolationand recovery of the M₂ BeH₄.

To illustrate, when the reaction involves pressure hydrogenating amixture of, say, lithium aluminum tetraethyl and a finely-dividedberyllium-titanium alloy, the solid reaction product normally willcontain the following components (the approximate densities of which areshown in parentheses):

Li₂ BeH₄ (0.70 g/cc)

LiAlH₄ (0.86˜0.92 g/cc)

LiH (0.78˜0.82 g/cc)

BeH₂ (0.65 g/cc)

Be (1.85 g/cc)

Al (2.70 g/cc)

Ti (4.50 g/cc)

By admixing this product with an inert diluent having a specific gravitybetween about 0.72 and about 0.78˜0.80 gram per milliliter, an operationpreferably conducted with an initial period of agitation followed by aperiod of standing in the quiescent state, the desired product (Li₂BeH₄) becomes physically separated from essentially all of the othersolid components which settle from the diluent. Thus the desired productis readily recovered, e.g., by decanting off the upper portion of thediluent containing the Li₂ BeH₄ (and BeH₂) solids. If desired thediluent may then be removed from the Li₂ BeH₄, e.g., by filtration,centrifugation, vacuum distillation, or the like.

When the same procedure is utilized in the production and recovery ofNa₂ BeH₄ by pressure hydrogenation of, say, a beryllium-titanium alloyand NaAlEt₄ or NaAlEt₃ H or NaAlEt₂ H₂ the solid reaction product willusually contain the following components (approximate densities againshown in parentheses):

Na₂ BeH₄ (0.9 g/cc)

NaAlH₄ (1.27 g/cc)

NaH (1.36 g/cc)

BeH₂ (0.65 g/cc)

Be (1.85 g/cc)

Al (2.70 g/cc)

Ti (4.50 g/cc)

Thus in this case the specific gravity of the diluent used for effectingthe separation should fall within the range of from about 0.92 to about1.2 and preferably from about 0.95 to about 1.05 gram per milliliter.

A few illustrative examples of inert diluents which may be used ineffecting the above separations include the following (approximatespecific gravities shown in parentheses):

n-decane (0.726)

2,3,3-trimethylpentane (0.726)

methylcyclohexane (0.769)

m-propyltoluene (0.86)

m-xylene (0.864)

toluene (0.866)

tetrahydronaphthalene (0.87)

o-xylene (0.88)

1,2,3,4-tetramethylbenzene (0.905)

1-methylnaphthalene (1.025)

o-nitrotoluene (1.16)

nitrobenzene (1.2)

If desired, the separations may be effected at below or above roomtemperature, although ordinary ambient temperature conditions arepreferred.

If heat is applied to the system during the separation step, convectioncurrents and the like should be avoided.

Besides providing a very simple way of effecting an otherwise difficultseparation and recovery operation, this invention has the advantage ofkeeping BeH₂ coproduct together with the dialkali metal berylliumtetrahydride product, both such materials having similar properties anduses and both usually being very desirable products. BeH₂ also can beseparated in a second step from a mixture of the two by using ahydrocarbon diluent with specific gravity less than 0.70 g/cc, such asn-pentane, n-hexane, or the like.

The beryllium employed in the process is preferably in sub-divided formsuch as flakes, chips, turnings, ribbon, powder, or the like. It may beused in relatively pure form. However in accordance with a preferredembodiment of this invention, the beryllium is utilized in the form of aberyllium-Group IVB metal alloy such as beryllium-titanium,beryllium-zirconium, beryllium-hafnium, beryllium-titanium-zirconium,beryllium-zirconium-hafnium, beryllium-titanium-zirconium-hafnium orlike alloys, provided the alloy contains a sufficient quantity ofberyllium to enable the desired reaction to take place. Preferred alloyscontain 50 weight percent or more of beryllium.

It is believed that the Group IVB metal, especially titanium, exerts adistinct reaction promoting or catalytic effect and thus greatlyaccelerates the formation of the desired dialkali metal berylliumtetrahydrides during the pressure hydrogenation.

In addition, the presence of the Group IVB metal in an alloy withberyllium results in the presence in the reaction product of densemetallic particles (e.g., unreacted beryllium-Group IVB metal alloy, aswell as the Group IVB metal itself). The high density of such particles(4.5 g/cc for titanium, 6.4 g/cc for zirconium, and 11.4 g/cc forhafnium) provides a relatively rapid rate of settling in the hydrocarbondiluent and this not only enhances the desired separation but enablesthese valuable Group IVB metal-containing metallic particles to becollected in relatively pure form (e.g., by allowing the settling tooccur in a tall column whereby the particles of greatest density (e.g.,Ti, Zr or Hf) settle even more rapidly than the other particles thatsettle to the bottom.

The alkali metal aluminum complexes useful in the process comprise thealkali metal aluminum hydrocarbyl trihydrides, MAlRH₃ ; the alkali metalaluminum dihydrocarbyl dihydrides, MAlR₂ H₂ ; the alkali metal aluminumtrihydrocarbyl hydrides, MAlR₃ H; the alkali metal aluminumtetrahydrocarbyls, MAlR₄ ; and mixtures of any two or three or all fourof these. The hydrocarbyl groups, R, may contain any suitable number ofcarbon atoms and may be aliphatic, cycloaliphatic, and/or aromatic. Rmay also be any suitably inert heterocyclic group, (groups in which thehetero atom(s) may be nitrogen, oxygen, etc.) or R may be any otherinert substituted or unsubstituted cyclic or acyclic organic group whichdoes not interfere with the desired reaction.

Exemplary hydrocarbyl compounds of this type include lithium aluminumethyl trihydride, sodium aluminum butyl trihydride, potassium aluminummethyl trihydride, lithium aluminum phenyl trihydride, sodium aluminumcyclohexyl trihydride, sodium aluminum benzyl trihydride, potassiumaluminum octadecyl trihydride, lithium aluminum phenethyl trihydride,lithium aluminum dimethyl dihydride, sodium aluminum dipentyl dihydride,potassium aluminum diethyl dihydride, sodium aluminum bis(p-tolyl)dihydride, sodium aluminum bis(cyclopentyl) dihydride, sodium aluminumdibenzyl dihydride, potassium aluminum bis(hexadecyl) dihydride, lithiumaluminum bis(phenethyl) dihydride, lithium aluminum ethyl methyldihydride, lithium aluminum trimethyl hydride, sodium aluminum tripropylhydride, potassium aluminum triethyl hydride, sodium aluminumtris(p-ethylphenyl) hydride, sodium aluminum bis(cyclopentyl) ethylhydride, sodium aluminum tribenzyl hydride, potassium aluminumtris(tetradecyl) hydride, lithium aluminum tris(cyclopropylcarbinyl)hydride, lithium aluminum tetraethyl, lithium aluminum tetrabutyl,sodium aluminum tetrabutyl, potassium aluminum tetramethyl, lithiumaluminum tetraphenyl, sodium aluminum tetracyclohexyl, sodium aluminumdibenzyl dimethyl, potassium aluminum tetraoctadecyl, lithium aluminumphenethyl triethyl, and the like. Sodium aluminum tetraethyl andequivalent sodium aluminum tetraalkyls, as well as their lithiumcounterparts are the preferred reactants.

The relative proportions between the beryllium and the alkali metalaluminum complex are not critical. However since the amount of thedesired alkali metal beryllium tetrahydride formed is normally limitedby the amount of the alkali metal aluminum complex employed, it ispreferred to use this reactant in excess. For best results it ispreferred to employ at least two gram moles of the alkali metal aluminumcomplex per gram equivalent of beryllium used.

It is desirable and convenient to use an excess of hydrogen.

Hydrogen pressures of at least about 1,000 psig will normally beemployed, although in some cases reaction may proceed at lowerpressures. Preferably the atmosphere is composed essentially entirely ofdry hydrogen, although mixtures of hydrogen and other suitable gaseousmaterials, such as nitrogen, argon, etc., may be used if desired.Temperatures in the range of about 100°to about 350° C., and preferablyin the range of about 125°to about 275° C., may be used. On the basis ofavailable information, there is nothing critical about these reactionconditions provided of course that in any given case the pressure andtemperature conditions selected result in the formation of the desiredalkali metal beryllium tetrahydride and do not cause its decomposition.

The reaction may be conducted in bulk (i.e., no diluent is introducedinto the reaction system). However it is deemed preferable to carry outthe reaction in a suitable innocuous liquid diluent such as ahydrocarbon. Alkanes, cycloalkanes and aromatics are desirable materialsfor this use.

Use of agitation to insure intimate contact among the reactioncomponents is recommended.

The Drawing illustrates in schematic fashion one preferred way by whichthe process of this invention may be practiced. Into a pressure reactor10 equipped with an agitator 12 and heating means (not shown) arecharged under an atmosphere of dry nitrogen, finely divided berylliummetal 13 (preferably in the form of an alloy such as Be-Ti), aninnocuous essentially anhydrous diluent 15 such as toluene, alkali metalaluminum complex 17 such as LiAlEt₄, NaAlEt₄, or KAlEt₄ and the sealedreactor 10 is pressurized with hydrogen 19 and heated with agitation toa suitable reaction temperature, e.g., 150° C. After a reaction periodof 18 hours the contents of reactor 10 are transferred (as indicated byline 16) in the absence of moisture and air to centrifuge 20. Thereaction solution, which comprises the innocuous diluent andhydrocarbon-soluble reaction coproducts such as unreacted alkali metalaluminum complex and derivatives thereof (e.g., Et_(n) AlH_(3-n) where nis 3 or less), is discharged as at 22. The solid reaction productdischarged from centrifuge 20 as at 24 is transferred to settling tower30 containing an anhydrous inert diluent of appropriate specific gravityintroduced at 26. The resultant solids/diluent mixture is agitated intower 30 by means of stirrer 32 to insure that the solids are welldispersed in the diluent. The stirrer 32 is turned off and a physicalseparation between the solid phases is caused to take place in thetower, the solids of specific gravity greater than that of the diluentsettle to the bottom as at 33 whereas the solids of specific gravityless than that of the diluent (e.g., Li₂ BeH₄,Na₂ BeH₄, K₂ BeH₄, BeH₂,etc.) rise to the top as at 35.

The dense settled solids and a portion of the diluent are withdrawn fromthe bottom of tower 30 as at 34, and the less dense solids and a portionof the diluent in and on which they are suspended are transferred (asindicated by line 37) under anhydrous, air-free conditions to asolid-liquid separator 40 such as a centrifuge, filter, vacuum still orthe like. The diluent is separated and removed as indicated by line 43and the desired product solids composed predominantly of M₂ BeH₄ arerecovered as indicated by line 45 and, if desired, are subjected todrying at 50 under suitable anhydrous, air-free conditions, preferablyat a suitably elevated temperature such as 50° to 150° C. in vacuo or atatmospheric pressure.

The alkali metal beryllium tetrahydrides are useful as portable sourcesof hydrogen gas and as reducing agents in a variety of chemicalsynthesis reactions. Other known uses for the materials are referred toin U.S. Pat. No. 3,647,399 to Ashby and Kobetz, the disclosure of whichis incorporated herein.

This invention is susceptible to considerable variation in its practicein accordance with the true spirit and scope of the ensuing claims.

I claim:
 1. In a process which comprises subjecting a mixture ofberyllium and an alkali metal aluminum complex of the formula

    MAlR.sub.m H.sub.n

wherein M is an alkali metal, R is a hydrocarbyl group, m is an integerfrom 1 to 4, n is an integer from 0 to 3, the total of m and n being 4,to a pressurized atmosphere of hydrogen and an elevated temperaturethereby producing a solid reaction product composed of M₂ BeH₄ and othersolid components, the improvement which comprises (i) mixing the solidreaction product and an inert liquid diluent having a specific gravityabove that of the M₂ BeH₄ but below that of essentially all of the othersolid components, (ii) effecting in said diluent a separation betweenthe M₂ BeH₄ and essentially all of such other solid components, and(iii) recovering the M₂ BeH₄.
 2. The process of claim 1 wherein m is 4and n is
 0. 3. The process of claim 1 wherein M is lithium.
 4. Theprocess of claim 1 wherein M is sodium.
 5. The process of claim 1wherein M is lithium and said specific gravity is between about 0.72 andabout 0.78 gram per milliliter.
 6. The process of claim 1 wherein M issodium and said specific gravity is between about 0.95 and about 1.05gram per milliliter.
 7. In a process which comprises subjecting amixture of a beryllium-titanium alloy and an alkali metal aluminumcomplex of the formula

    MAlR.sub.m H.sub.n

wherein M is an alkali metal, R is a hydrocarbyl group, m is an integerfrom 1 to 4, n is an integer from 0 to 3, the total of m and n being 4,to a pressurized atmosphere of hydrogen and an elevated temperaturethereby producing a solid reaction product composed of M₂ BeH₄ and othersolid components, the improvement which comprises (i) mixing the solidreaction product and an inert liquid hydrocarbon diluent having aspecific gravity above that of the M₂ BeH₄ but below that of essentiallyall of the other solid components, (ii) effecting in said diluent aseparation between the M₂ BeH₄ and essentially all of such other solidcomponents, and (iii) recovering the M₂ BeH₄.
 8. The process of claim 7wherein m is 4 and n is
 0. 9. The process of claim 7 wherein M islithium.
 10. The process of claim 7 wherein M is sodium.
 11. The processof claim 7 wherein M is lithium and said specific gravity is betweenabout 0.72 and about 0.78 gram per milliliter.
 12. The process of claim7 wherein M is sodium and said specific gravity is between about 0.95and about 1.05 gram per milliliter.
 13. In a process which comprisessubjecting an agitated mixture of an inert hydrocarbon diluent, aberyllium-titanium alloy and an alkali metal aluminum complex of theformula

    MAlR.sub.m H.sub.n

wherein M is an alkali metal, R is a hydrocarbyl group, m is an integerfrom 1 to 4, n is an integer from 0 to 3, the total of m and n being 4,to a pressurized atmosphere of hydrogen and an elevated temperaturethereby producing a solid reaction product composed of M₂ BeH₄ and othersolid components in admixture with said diluent, the improvement whichcomprises (i) separating the solid reaction product from the diluent,(ii) forming a mixture of the solid reaction product and an inert liquidhydrocarbon diluent having a specific gravity above that of the M₂ BeH₄but below that of essentially all of the other solid components, (iii)effecting in said diluent a separation between the M₂ BeH₄ andessentially all of such other solid components, and (iv) recovering theM₂ BeH₄.
 14. The process of claim 13 wherein m is 4 and n is
 0. 15. Theprocess of claim 13 wherein M is lithium.
 16. The process of claim 13wherein M is sodium.
 17. The process of claim 13 wherein M is lithiumand said specific gravity is between about 0.72 and about 0.78 gram permilliliter.
 18. The process of claim 13 wherein M is sodium and saidspecific gravity is between about 0.95 and about 1.05 gram permilliliter.